Electrically conducting polyaniline (PANI)-magnetic oxide (Fe3O4) composites with electrical and ferromagnetic behaviors were synthesized by the way of emulsion polymerization using dodecyl benzene sulfonic acid (DBSA) as a surfactant and dopant, and ammonium persulfate (APS) as the oxidant. The microstructures and electromagnetic parameters of the composites were investigated by the TEM、FTIR、 XRD 、permittivity and permeability measures. The results showed that the average diameter of the Fe3O4/PANI/DBSA nanocomposites is about 120 nm when the molar ratio of the DBSA to An is 1.0. The contents of DBSA have a great influence on the conductivity and crystallization. The real (ε′) and imaginary (ε″) part of permittivity are increased with the increase of DBSA and the is ε″ invariable when it reaches some values. The real part of permeability (μ′)is about constant with the different contents of DBSA and the imaginary part of permeability(μ″) has a fluctuant change with the increment of DBSA. The different dissipative mechanisms were discussed to explain the varieties.